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| United States Patent |
5,140,826
|
|
Hanson
, et al.
|
August 25, 1992
|
Method of operating a transport refrigeration unit
Abstract
A method of operating a transport refrigeration system having a refrigerant
compressor driven by an internal combustion engine. Microprocessor based
electrical control maintains the temperature of a conditioned space at a
desired set point via heating, cooling and null cycles, with the engine
being started and stopped, as required. During the engine starting
process, a suction line modulation valve, if used, is closed, engine
pre-heat time is selected, including using engine temperature to access a
look-up table, and current draw is checked during pre-heat. Excessive
current terminates pre-heat. Control diagnostics checks the voltage level
on both sides of a refrigerant high pressure switch, before initiating
engine cranking. Prior to stopping the engine, a control option initiates
a heating cycle for a short time when null is being entered from a cooling
cycle, to warm the evaporator and prevent premature starting of the
engine.
| Inventors:
|
Hanson; Jay L. (Bloomington, MN);
Howland; Leland L. (Belle Plaine, MN)
|
| Assignee:
|
Thermo King Corporation (Minneapolis, MN)
|
| Appl. No.:
|
728665 |
| Filed:
|
July 11, 1991 |
| Current U.S. Class: |
62/115; 62/126; 62/228.3; 73/117.2; 123/142.5R |
| Intern'l Class: |
F02N 017/02 |
| Field of Search: |
123/179.6,179.21,142.5 R,142.5 E
62/228.3,323.1,230,115,126,217
73/117.2
|
References Cited
U.S. Patent Documents
| 4050297 | Sep., 1977 | Pettingell et al. | 73/117.
|
| 4419866 | Dec., 1983 | Howland | 62/228.
|
| 4663725 | May., 1987 | Truckenbrod et al. | 364/505.
|
| 4878465 | Nov., 1989 | Hanson et al. | 123/179.
|
| 4918932 | Apr., 1990 | Gustafson et al. | 62/89.
|
| 4977751 | Dec., 1990 | Hanson | 62/217.
|
| 4977752 | Dec., 1990 | Hanson | 62/213.
|
| 5063513 | Nov., 1991 | Shank et al. | 123/142.
|
Primary Examiner: Wayner; William E.
Attorney, Agent or Firm: Lackey; D. R.
Claims
We claim:
1. A method of operating a transport refrigeration unit which includes
microprocessor based electrical control for controlling the temperature of
a conditioned space via heating, cooling and null cycles, and a
refrigerant circuit which includes a compressor, a condenser, and an
evaporator, and including a prime mover arrangement for driving the
compressor which includes an internal combustion engine which is
automatically started and stopped by the electrical control in response to
predetermined conditions, comprising the steps of:
sensing the temperature of the engine prior to each start thereof,
pre-heating the engine prior to each start thereof,
providing predetermined minimum and maximum engine pre-heat times for first
and second predetermined engine temperatures, respectively,
providing a look-up table which relates engine temperature to pre-heat time
for engine temperatures between the first and second predetermined values,
providing a plausible range for the engine temperature,
determining if the sensed temperature is in the plausible range,
said pre-heating step heating the engine for the predetermined maximum
pre-heat time when the sensed temperature is not in the plausible range,
determining the location of the sensed temperature relative to the first
and second predetermined engine temperatures,
said pre-heating step heating the engine for the minimum pre-heat time when
the sensed temperature is at, and when it is above, the first
predetermined temperature,
said pre-heating step heating the engine for the maximum pre-heat time when
the sensed temperature is at, and when it is below, the second
predetermined temperature,
and accessing the look-up table when the sensed engine temperature is
between the first and second predetermined values, to provide a pre-heat
time related to the specific engine temperature,
said pre-heating step heating the engine for the pre-heat time obtained
from the look-up table when the sensed engine temperature is between the
first and second predetermined values.
2. The method of claim 1 including the step of setting an alarm when the
sensed temperature is not in the plausible range.
3. The method of claim 1 wherein the preheating step includes the steps of:
heating the engine electrically,
measuring the magnitude of the resulting current flow a predetermined
period of time after the pre-heating step is initiated,
determining if the measured current magnitude exceeds a predetermined
value,
and terminating the pre-heating step in response to the determining step
when the current magnitude exceeds the predetermined value.
4. The method of claim wherein the preheating step includes the steps of:
heating the engine electrically,
measuring the magnitude of the resulting current flow a predetermined
period of time after the pre-heating step is initiated,
determining if the measured current magnitude is within a predetermined
normal range,
setting an alarm when the measured current magnitude is not within the
predetermined range,
determining if the measured current magnitude exceeds a predetermined value
when the measured current is not within the predetermined range,
and terminating the pre-heat step in response to a determination that the
measured current magnitude exceeds the predetermined value.
5. The method of claim 1 wherein the refrigerant circuit includes a high
pressure cut-out switch having first and second sides connected in a
control circuit in which voltage is applied to the high pressure cut-out
switch via a predetermined relay, with the high pressure cut-out switch
being closed until pressure exceeds a predetermined value, including the
steps of:
detecting the voltage level on each side of the high pressure cut-out
switch during the process of starting the internal combustion engine,
setting a first alarm indicating high refrigerant pressure, in response to
detecting voltage on only one side of the high pressure cut-out switch,
setting a second alarm indicating failure of the predetermined relay in
response to absence of voltage on either side of the high pressure cut-out
switch,
and terminating the starting of the engine in response to the setting of
either the first or second alarms.
6. The method of claim 1 wherein the transport refrigeration unit includes
a suction line modulation valve, and including the step of closing the
suction line modulation valve prior to starting the engine.
7. The method of claim 1 wherein the control circuit includes a timer, a
battery and an alternator, and the engine includes a starter for cranking
the engine, a low oil pressure switch, means for driving the alternator,
and an engine speed sensor, and including the steps of:
detecting engine speed during the cranking thereof,
timing the cranking of the engine,
determining if the engine oil pressure is low,
determining if the battery is being charged by the alternator,
detecting failure of the engine speed to reach a first predetermined value
within a first predetermined period of time, and, in response to such a
detection:
setting a first alarm indicating failure of the engine to crank when the
oil pressure is low and the battery is not being charged,
setting a second alarm indicating failure of the low oil pressure switch
when the oil pressure is low and the battery is being charged,
and setting a third alarm indicating failure of the engine speed sensor
when the oil pressure is not low and the battery is being charged.
8. The method of claim 7 including the steps of:
detecting failure of the engine speed to reach a second predetermined
value, which is higher than the first predetermined value, within a second
predetermined period of time, which is greater than the first
predetermined period of time, and, in response to such a detection:
setting a fourth alarm indicating failure of the engine to start, when the
oil pressure is low and the battery is not being charged,
setting the second alarm indicating failure of the low oil pressure switch,
when the oil pressure is low and the battery is being charged,
and setting the third alarm indicating failure of the engine speed sensor
when the oil pressure is not low and the battery is being charged.
9. The method of claim 1 wherein the engine is turned off during a null
cycle, and including steps of:
determining if a requested null cycle will be entered from a heat cycle or
a cool cycle,
and initiating a heat cycle for a predetermined short period of time prior
to entering a requested null cycle, to warm the evaporator coil, when the
determining step finds a requested null cycle will be entered from a
cooling cycle.
10. A method of operating a transport refrigeration unit which includes
microprocessor based electrical control for controlling the temperature of
a conditioned space via heating, cooling and null cycles, and a
refrigerant circuit which includes a compressor, a condenser, and an
evaporator, and including a prime mover arrangement for driving the
compressor which includes an internal combustion engine, and a starting
circuit for the internal combustion engine which includes a battery, with
the internal combustion engine being automatically started and stopped by
the electrical control in response to predetermined conditions, comprising
the steps of:
sensing the temperature of the engine prior to each start thereof,
pre-heating the engine electrically via a pre-heat circuit which includes
the battery, prior to each start thereof,
providing a DC shunt disposed to measure battery current,
reading the magnitude of the battery electrical current via the DC shunt,
with said reading step being initiated a predetermined period of time
after the pre-heating step if initiated,
comparing the magnitude of the electrical current reading with a
predetermined value,
and terminating the pre-heating step in response to the comparing step when
the magnitude of the electrical current reading exceeds the predetermined
value.
11. The method of claim 10 wherein the refrigerant circuit includes a
suction line modulation valve, and including the step of closing the
suction line modulation valve prior to starting the engine.
12. A method of operating a transport refrigeration unit which includes
microprocessor based electrical control for controlling the temperature of
a conditioned space via heating, cooling and null cycles, and a
refrigerant circuit which includes a compressor, a condenser, and an
evaporator, and including a prime mover arrangement for driving the
compressor which includes an internal combustion engine which is
automatically started and stopped by the electrical control in response to
predetermined conditions, comprising the steps of:
sensing the temperature of the engine prior to each start thereof,
pre-heating the engine electrically prior to each start thereof,
measuring the magnitude of the resulting current flow a predetermined
period of time after the pre-heating step is initiated,
determining if the measured current magnitude is within a predetermined
normal range,
setting an alarm when the measured current magnitude is not within the
predetermined range,
determining if the measured current magnitude exceeds a predetermined value
when the measured current is not within the predetermined range,
and terminating the pre-heat step in response to a determination that the
measured current magnitude exceeds the predetermined value.
13. The method of claim 12 wherein the refrigerant circuit includes a
suction line modulation valve, and including the step of closing the
suction line modulation valve prior to starting the engine.
14. A method of operating a transport refrigeration unit which includes
microprocessor based electrical control for controlling the temperature of
a conditioned space via heating, cooling and null cycles, with the control
circuit including a high pressure cut-out switch having first and second
sides connected in a control circuit in which voltage is applied to the
high pressure cut-out switch via a predetermined relay, with the high
pressure cut-out switch being closed until pressure exceeds a
predetermined value, and a refrigerant circuit which includes a
compressor, a condenser, and an evaporator, and including a prime mover
arrangement for driving the compressor which includes an internal
combustion engine which is automatically started and stopped by the
electrical control in response to predetermined conditions, comprising the
steps of:
detecting the voltage level on each side of the high pressure cut-out
switch during the process of starting the internal combustion engine,
setting a first alarm indicating high refrigerant pressure, in response to
detecting voltage on only one side of the high pressure cut-out switch,
setting a second alarm indicating failure of the predetermined relay in
response to absence of voltage on either side of the high pressure cut-out
switch,
and terminating the starting of the engine in response to the setting of
either the first or second alarms.
15. The method of claim 14 wherein the refrigerant circuit includes a
suction line modulation valve, and including the step of closing the
suction line modulation valve prior to starting the engine.
16. A method of operating a transport refrigeration unit which includes a
control circuit for controlling the temperature of a conditioned space via
heating, cooling and null cycles, with the control circuit including a
timer, a battery and an alternator, and a refrigerant circuit which
includes a compressor, a condenser, and an evaporator, and including a
prime mover arrangement for driving the compressor which includes an
internal combustion engine which is automatically started and stopped by
the control circuit in response to predetermined conditions, with the
engine including a starter for cranking the engine, a low oil pressure
switch, means for driving the alternator, and an engine speed sensor,
comprising the steps of:
detecting engine speed during the cranking thereof,
timing the cranking of the engine,
determining if the engine oil pressure is low, determining if the battery
is being charged by the alternator,
detecting failure of the engine speed to reach a first predetermined value
within a first predetermined period of time, and, in response to such a
detection:
setting a first alarm indicating failure of the engine to crank when the
oil pressure is low and the battery is not being charged,
setting a second alarm indicating failure of the low oil pressure switch
when the oil pressure is low and the battery is being charged,
and setting a third alarm indicating failure of the engine speed sensor
when the oil pressure is not low and the battery is being charged.
17. The method of claim 16 including the steps of:
detecting failure of the engine speed to reach a second predetermined
value, which is higher than the first predetermined value, within a second
predetermined period of time, which is greater than the first
predetermined period of time, and, in response to such a detection:
setting a fourth alarm indicating failure of the engine to start, when the
oil pressure is low and the battery is not being charged,
setting the second alarm indicating failure of the low oil pressure switch,
when the oil pressure is low and the battery is being charged,
and setting the third alarm indicating failure of the engine speed sensor
when the oil pressure is not low and the battery is being charged.
18. The method of claim 16 wherein the refrigerant circuit includes a
suction line modulation valve, and including the step of closing the
suction line modulation valve prior to starting the engine.
19. A method of starting an internal combustion engine which is connected
to drive a refrigerant compressor which is connected in a closed
refrigerant circuit having a condenser, an evaporator, and a controllable
suction line modulation valve, comprising the steps of:
closing the suction line modulation valve,
selecting an engine pre-heat time responsive to engine temperature,
pre-heating the engine electrically for the selected pre-heat time,
measuring the pre-heat current,
setting the pre-heat time elapsed when the measuring step indicates the
pre-heat current exceeds a predetermined value,
checking the refrigerant circuit for excessive pressure,
and cranking the engine after the pre-heat time elapses and the checking
step indicates the refrigerant pressure is not excessive.
20. The method of claim 19 wherein the compressor includes a high pressure
cut-out switch having first and second sides connected in a control
circuit, and the step of checking the refrigerant circuit for excessive
pressure includes the steps of:
detecting the voltage level on both sides of the high pressure cut-out
switch,
and enabling the cranking step only when voltage is detected on both sides
of the high pressure cut-out switch.
Description
TECHNICAL FIELD
The invention relates in general to transport refrigeration units, and more
specifically to transport refrigeration units which have a compressor
prime mover which includes an internal combustion engine operable in a
cycling or on-off mode.
BACKGROUND ART
U.S. Pat. No. 4,419,866, which is assigned to the same assignee as the
present application, discloses a transport refrigeration system in which a
Diesel engine which drives a refrigerant compressor may be selectively
operated in either a continuous or a start-stop mode. In the start-stop
mode, the Diesel engine is under the control of a refrigeration
thermostat, being stopped and re-started as the temperature of a
controlled space enters and leaves predefined temperature bands relative
to a selected temperature set point.
U.S. Pat. No. 4,878,465, which is also assigned to the same assignee as the
present application, discloses improved electrical control for
automatically starting a Diesel engine, which simplified the control and
improved the logic of the '866 patent. A thermistor in the engine coolant
controls the engine pre-heat time. A battery monitor control module
determines if the battery charge condition is at a level sufficient to
permit the engine to stop. An electronic temperature control module or
thermostat control the temperature of the served space, similar to the
'866 patent.
While the systems of the '866 and '465 patents perform well, it would be
desirable, and it is an object of the present invention, to integrate and
consolidate all of the functions of the separate control modules into one
controlling function, such as provided by a computer, and more
specifically a microprocessor, while further enhancing and improving the
control of a transport refrigeration unit.
U.S. Pat. Nos. 4,663,725 and 4,918,932, which are assigned to the same
assignee as the present application, disclose the use of microprocessor
based refrigeration control for use with transport refrigeration systems,
with the controlling functions being related to aspects of such systems
other than the prime mover.
SUMMARY OF THE INVENTION
Briefly, the present invention is a method of operating a transport
refrigeration unit with microprocessor based electrical control, for
controlling the temperature of a conditioned space via selectable
continuous and start-stop modes. The continuous mode controls temperature
in the served space via heating and cooling cycles, and the start-stop
mode controls temperature in the served space via heating, cooling and
null cycles.
The transport refrigeration unit includes a refrigerant compressor
connected in a closed refrigerant circuit which also includes a condenser,
and an evaporator. A controllable suction line modulation valve may
optionally be provided in a suction line between the evaporator and
compressor. The prime mover arrangement for the compressor includes an
internal combustion engine, such as a Diesel engine, and the drive
arrangement may optionally include a stand-by electric motor for driving
the compressor when the associated container, truck or trailer is
stationary and located near a source of electrical potential.
Each time the Diesel engine is started, the microprocessor checks to see if
the unit will be operating with a controllable suction line valve, and if
so, the suction line valve is closed before the engine is cranked to
reduce the compressor load on the engine during starting.
Each time the Diesel engine is started, the microprocessor checks the value
of a sensor disposed to measure the temperature of the Diesel engine
coolant. The microprocessor compares the value with a pre-stored plausible
range of values for this sensor. If the sensor value is outside the
plausible range, the microprocessor automatically assigns a predetermined
maximum pre-heat time and an alarm is set which will indicate to the
operator and/or service personnel that the coolant sensor is faulty. If
the sensor value is within the plausible range, the value is used to
access a pre-stored look-up table to obtain the correct pre-heat time for
the engine The look-up table may include maximum and minimum times for
temperatures beyond a predetermined temperature range, or the
microprocessor may preliminarily compare the sensor value to the
predetermined temperature range and automatically assign the maximum
pre-heat time or the minimum pre-heat time, as required, using the look-up
table only for sensor values within the predetermined temperature range.
After the engine pre-heat time has been determined, the microprocessor
initiates engine pre-heat by energizing electrical glow plugs. After a
short period of time selected to enable the glow plug current to
stabilize, the microcomputer checks the voltage across a DC shunt in the
system battery circuit to determine if the glow plug current is in a
proper predetermined range. If it is not in the desired range, an
appropriate alarm is set, and the microprocessor then determines if the
current draw is too high to permit pre-heat to continue. If the current
draw exceeds a predetermined maximum allowable value, the pre-heat time is
set "elapsed", and the engine starting process is continued, to attempt an
engine start without completing the selected pre-heat time
The microprocessor then enables a circuit which includes a relay RUN, which
establishes a control circuit which includes a fuel solenoid and a high
pressure cutout. The high pressure cut-out is disposed to monitor
refrigerant pressure in the high pressure side of the refrigerant circuit,
such as near the condenser. Instead of merely monitoring the cut-out
switch to see if it is closed or open, the microprocessor checks the
voltage level on each side of the switch. If voltage is detected on only
one side of the switch, an alarm is set which indicates high refrigerant
pressure. If voltage is detected on neither side of the switch, an alarm
is set which indicates failure of the relay RUN. If either alarm is set,
the engine starting process is terminated.
If the voltage level check on both sides of the high pressure cut-out
switch indicates no refrigerant pressure problem and no problem with the
relay RUN, the microprocessor initiates the cranking of the engine The
microprocessor then logically combines time, engine speed, oil pressure,
and polarity of the current flow relative to the battery to determine
whether the engine has started, and to generate various fault codes when a
problem is encountered. The microprocessor detects the failure of the
engine speed to reach a first predetermined value within a first
predetermined period of time, and in response to such detection:
1) a first alarm is set which indicates failure of the engine to crank when
an oil pressure sensor switch indicates low oil pressure and the polarity
of the DC shunt voltage indicates the battery is not being charged; or
2) a second alarm is set which indicates failure of the oil pressure sensor
switch when the oil pressure sensor switch indicates low oil pressure and
the polarity of the DC shunt voltage indicates the battery is being
charged; or
3) a third alarm is set which indicates failure of the engine speed sensor
when the oil pressure sensor switch indicates the oil pressure is not low
and the polarity of the DC shunt voltage indicates the battery is being
charged.
If the engine speed reaches the first predetermined value within the first
predetermined period of time, the process is repeated relative to a second
engine speed and a second predetermined period of time, setting alarms
similar to those just described when the engine speed fails to reach the
requisite speed within the requisite time. The first alarm is coded to
indicate "failure to start", rather than "failure to crank", since the
engine did meet the first speed-time test, and obviously the engine did
crank.
In a selectable option, before the microprocessor shuts the engine down to
enter a null condition during which the served space requires neither
cooling or heating to satisfy the selected set point temperature, the
microprocessor determines if the null condition will be entered from a
cooling cycle or from a heating cycle. If the null condition will be
entered from a cooling cycle, the microprocessor switches the transport
refrigeration unit to a heating cycle just before stopping the engine, for
a period of time selected to just warm the evaporator coil. This feature
prevents premature starting of the engine due to the cold surface of the
evaporator coil cooling a load space temperature sensor, which would
unnecessarily result in the control system re-starting the engine to
provide heat to the served space.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will become more apparent by reading the following detailed
description in conjunction with the drawings, which are shown by way of
example only, wherein:
FIG. 1 is a partially block and partially schematic diagram of a
refrigeration system which may be controlled by the methods of the
invention;
FIGS. 2A and 2B may be assembled to provide an electrical schematic diagram
which implements the methods of the invention;
FIG. 3 is a block diagram of a time driven "real time case select" function
performed by the microprocessor shown in FIGS. 1 and 2;
FIG. 4 is a flow chart illustrating a "mode decision" function performed by
the microprocessor;
FIG. 5 is a flow chart of a "mode case select" function performed by the
microprocessor;
FIGS. 6A and 6B may be assembled to provide a flow chart of an engine start
function which sets forth some of the methods of the invention;
FIG. 7 is a graph which sets forth engine coolant temperature versus
pre-heat time, illustrating graphically a look-up table of pre-heat times
versus coolant temperatures;
FIG. 8 is a flow chart of a modulation valve start routine executed by the
microprocessor when the engine is to be started in order to close a
suction line modulation valve and reduce starting load on the engine;
FIG. 9 is a graph which sets forth a modulation valve current versus time
pattern followed by the flow chart function shown in FIG. 8;
FIG. 10 is a flow chart of a "continuous" mode of operating the transport
refrigeration system shown in FIG. 1;
FIG. 11 is a flow chart of a "start-stop" mode of operating the transport
refrigeration system shown in FIG. 1;
FIG. 12 is a chart setting forth a return-air control algorithm utilized by
the start-stop mode shown in FIG. 11, when the set point is greater than
24 degrees F;
FIG. 13 is a chart setting forth a return-air control algorithm utilized by
the start-stop mode shown in FIG. 11, when the set point is 24 degrees and
below; and
FIGS. 14A and 14B may be assembled to provide a flow chart which implements
going from a cooling cycle into a null cycle, as set forth in the
algorithms of FIGS. 12 and 13.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawing, and to FIG. 1 in particular, there is shown a
transport refrigeration unit 20 which may be controlled according to the
methods of the invention. Refrigeration unit 20 may be mounted on a
container, truck, or trailer, such as on a wall 22 thereof, for example.
Refrigeration unit 20 has a closed fluid refrigerant circuit 24 which
includes a refrigerant compressor 26 driven by a prime mover arrangement
28. Prime mover arrangement 28 includes an internal combustion engine 30,
and it may optionally include a stand-by electric motor 32. Engine 30 and
motor 32 are coupled to compressor 26 by a suitable clutch or coupling 34
which disengages engine 30 while motor 32 is operative. A selector 35
selects the desired prime mover.
Discharge ports of compressor 26 are connected to an inlet port of a
three-way valve 36 via a discharge service valve 38 and a hot gas line 40.
The functions of three-way valve 36, which selects heating and cooling
cycles, may be provided by two separate valves, if desired. Three-way
valve 36 has a first output port 42, which is selected to initiate a
cooling cycle, with the first output port 42 being connected to the inlet
side of a condenser coil 44. Three-way valve 36 has a second outlet port
46, which is selected to initiate a heating cycle, as will be hereinafter
described Expansion valve 58 is controlled by a thermal bulb 71 and an
equalizer line 73.
When three-way valve 36 selects the cooling cycle output port 42, it
connects compressor 26 in a first refrigerant circuit 48, which in
addition to condenser 44, includes a one-way condenser check valve CVI, a
receiver 50, a liquid line 52, a refrigerant drier 54, a heat exchanger
56, an expansion valve 58, a refrigerant distributor 60, an evaporator
coil 62, an optional controllable suction line modulation valve 64,
another path through heat exchanger 56, an accumulator 66, a suction line
68, and back to a suction port of compressor 26 via a suction line service
valve 70. The operative prime mover may be protected against overload by
controlling modulation valve 64 to provide the function of a conventional
compressor throttling valve, as taught by U.S. Pat. No. 4,977,751, which
is assigned to the same assignee as the present application; or, a
conventional compressor throttling valve may be disposed in suction line
68, as desired
When three-way valve 36 selects the heating cycle output port 46, it
connects compressor 26 in a second refrigerant circuit 72. The second
refrigerant circuit 72 by-passes condenser 44 and expansion valve 58,
connecting the hot gas output of compressor 26 to the refrigerant
distributor 60 via a hot gas line 74 and a defrost pan heater 76. A hot
gas by-pass solenoid valve 77 may be disposed in hot gas line 74. A
by-pass or pressurizing line 78 connects hot gas line 74 to receiver 50
via by-pass and check valves 80, to force refrigerant from receiver 50
into an active refrigerant circuit during heating and defrost cycles.
A conduit or line 82 connects three-way valve 36 to the low side of
compressor 26 via a normally closed pilot solenoid valve PS. When solenoid
valve PS is deenergized and thus closed, three-way valve 18 is spring
biased to select the cooling cycle output port 42. When evaporator 62
requires defrosting, and when the load being conditioned requires heat to
maintain set point, pilot solenoid valve PS is energized to allow the low
pressure side of compressor 26 to operate three-way valve 36 to select the
heating cycle output port 46.
A condenser fan or blower (not shown) causes ambient air 84 to flow through
condenser coil 44, with the resulting heated air 86 being discharged to
the atmosphere. An evaporator fan or blower (not shown) draws air 88,
called "return air", from a served space 90 whose air is to be
conditioned, through the evaporator coil 62, and the resulting cooled or
heated air 92, called "discharge air" is returned to the space 90. During
an evaporator defrost cycle, the evaporator fan or blower is not operated,
and a defrost air damper may be operated to close the discharge air path
to the conditioned space 90.
Transport refrigeration unit 20 is controlled by microprocessor based
electrical control 94 which includes a microprocessor 96 and electrical
control 98. Electrical control 98 includes relays, and the like, as will
be explained relative to FIGS. 2A and 2B. The microprocessor 96 receives
input signals from appropriate sensors, such as from a return air
temperature sensor 100 disposed in a suitable return air path 102, a
discharge air temperature sensor 104 disposed in a suitable discharge air
path 106, from a coil temperature sensor 108 disposed to sense the
temperature of the evaporator coil 62, from a refrigerant pressure sensor
or high pressure cut-out (HPCO) 110 disposed on the high side of the
refrigerant circuit 48, and from various engine sensors shown in FIG. 2B,
such as oil level sensor 112 , oil pressure sensor 114, engine coolant
temperature sensor 116, and engine speed sensor 118.
Microprocessor 96, among other things, controls modulation valve 64, hot
gas solenoid valve 77, and a throttle or high speed solenoid 120. Other
functions controlled by microprocessor 96 are shown in FIGS. 2A and 2B,
and will be hereinafter described
FIGS. 2A and 2B may be assembled to provide a detailed schematic diagram of
microprocessor based electrical control 94, which includes microprocessor
96 and control 98. As is well known, microprocessor 96 includes a
read-only memory (ROM) 122 for storing programs to be hereinafter
described, and a random access memory (RAM) 124 for software timers,
flags, input signals, output signals, and other values generated by the
operating programs Microprocessor 96 also has a display 125 for displaying
fault codes, indicator lights, and the like.
Electrical control 98 includes a battery 126 which has one side connected
to a first conductor 128 via a DC shunt 130, an on-off switch 132, and
normally closed contacts 134 of a protective reset switch SSW. The
remaining side of battery 126 is connected to conductor 136, which is
grounded. Control 98 further includes an alternator 138 driven by prime
mover 28; a starter motor 140, for cranking engine 30, which is controlled
by a starter solenoid 142 having associated normally open contacts 143, an
ignition switch 144, and a start relay 146 having associated normally open
contacts 147; and glow plug resistors (GP) 148, for pre-heating engine 30,
which are controlled by a pre-heat switch 150 and by a pre-heat relay 152
which has a set of normally open contacts 153.
Control 98 also includes a three-position switch 154 having two banks of
three terminals The three terminals, referring to their positions in FIG.
2A, include a center terminal, an upper terminal, and a lower terminal.
Switch 154, in the illustrated upper position which connects the center
terminal to the upper terminal in each bank, places unit 20 under control
of the microprocessor 96. The upper position provides voltage from
conductor 128 to a conductor 155.
An intermediate position of switch 154, in which the center terminal is not
connected to either the upper or lower terminals, is selected when the
microprocessor 96 is not utilized and the load in the conditioned space 90
is frozen. This switch position will cause unit 20 to operate continuously
in a low speed cool mode.
The lower position of switch 154 is selected when the microprocessor 96 is
not utilized and the load in the conditioned space is fresh. This position
of switch 154 will cause unit 10 to operate continuously, cycling between
heating and cooling cycles under the control of the hereinbefore mentioned
coil temperature switch 108. Coil temperature switch 108 is preset to
close at a predetermined coil temperature, such as 35 degrees F., to
energize the pilot solenoid PS and initiate a heating cycle, and to open
at a predetermined higher temperature, such as 38 degrees F., to
de-energize pilot solenoid PS and initiate a cooling cycle.
In addition to the relays already mentioned, control 98 includes a shutdown
relay 156, a run relay 158, a heat relay 160, a high speed relay 162, a
defrost damper relay 164, and a hot gas relay 166. Shutdown relay 156,
which has a set of normally closed contacts 168, is normally energized.
Shutdown relay 156 is de-energized to shut unit 10 down via its contacts
168 which close to ground the protective switch SSW and cause it to open
its contacts 134.
The run relay 158 has normally-closed and normally open contacts 170 and
172, respectively, connected to a mode selector switch 174 which has an
input connected to conductor 128. Selector switch 174 selects either a
continuous operating mode in which the prime mover 28 operates
continuously, or a cycling start-stop mode which includes starting and
stopping the prime mover 28. The normally-closed contacts 170 of run relay
158 are connected to the "continuous" position of selector switch 174, and
the normally-open contacts 172 of run relay 158 are connected to the
"cycling" position of selector switch 174. Contacts 170 or contacts 172
provide voltage to a conductor 175 from conductor 128 and selector switch
174.
Heat relay 160 has a set of normally open contacts 176 for controlling the
pilot solenoid PS. High speed relay 162 has a set of normally open
contacts 178 for controlling the high speed solenoid 120. Damper relay has
a set of normally closed contacts 180 and a set of normally open contacts
182, connected to control a defrost damper solenoid 184. Hot gas relay 166
is provided for controlling the hot gas solenoid valve 77 via a set of
normally open contacts 186, when a hot gas solenoid valve 77 is provided
in hot gas line 74.
Control 98 also includes an engine coolant temperature switch (high water
temperature- HWT) 190, which closes upon an excessive engine temperature,
and a low oil pressure switch (LOPS) 192 which is open as long as engine
pressure is normal. The closing of either switch 190 or 192 will shut unit
20 down via the manual reset switch SSW.
Microprocessor 96 senses the voltage across DC shunt 130 via conductors 194
and 196, and can thus determine the magnitude and polarity of battery
current. One polarity, which will be called positive, indicates the
battery 126 is being charged by alternator 138, which also indicates the
prime mover 28 is running. The other polarity, i.e. negative, indicates
the battery is discharging.
Microprocessor 96 also has a conductor 198 which senses the position of the
low oil pressure switch 192, conductors 200 and 202 which sense the
voltage level on first and second sides, respectively, of the high
refrigerant cut-out switch 110, a conductor 204 which senses whether or
not a modulation valve selector jumper 206 has connected conductor 204 to
system ground 136, a conductor 208 which senses whether or not a defrost
sensor switch 210 has operated, signifying the need for a defrost cycle,
and a conductor 211 which detects voltage on the damper solenoid 184.
Microprocessor 96 has a plurality of output conductors for controlling
various functions, including conductors 212, 214, 216, 218, 220, 222, 224
and 226 for respectively controlling the operation of start relay 146,
pre-heat relay 152, shutdown relay 156, damper relay 164, high speed relay
162, run relay 158, heat relay 160, and hot gas relay 166. A conductor 228
is also provided for controlling the current level in the modulation valve
64.
Microprocessor 96 is time driven, with a "real time case select" function
230, shown in FIG. 3, being repeated continuously. As the microprocessor
functions are described, only those necessary to understanding the
invention will be described in detail. Certain of the functions shown in
block form, may be described in detail and claimed in concurrently filed
application Ser. Nos. 07/728,464; 07/728,463; 07/778,477.
Function 230 is entered at 232 and step 234 performs analog to digital
conversions of the analog inputs from various analog sensors. Step 236
performs a mode decision function which will be hereinafter described
relative to FIG. 4. Step 238 takes care of providing the necessary digital
signals which control various functions of unit 20, step 240 receives
digital inputs from various sensed functions, and step 242 receives the
engine speed input from RPM sensor 118. The program then returns to step
234 and upon reaching step 238 during the second pass, the program goes to
step 244 which takes care of setting the proper current level in the
modulation valve 64. Steps 234, 236 and 238 are then repeated, adding step
246 on the third pass, which updates microprocessor display 125, such as
status displays, as well as displays which set forth any alarm codes which
may have been set. Step 248 is added on the fourth pass, which performs
certain system checks, step 250 is added on the fifth pass, which performs
certain real time checks, step 252 is added on the sixth pass, which
performs a unit running check, step 254 is added on the seventh pass,
which performs certain alert or alarm functions, step 256 is added on the
eight pass, which performs certain timing functions, step 258 is added on
the ninth pass, which performs an error deviation function, and step 260
is added on a tenth pass, which checks the sensors for failure. Program
230 then repeats.
The mode decision program function 236, shown in FIG. 4, is entered at 262
and step 264 checks to see if microprocessor control has been selected via
the three position selector switch 154. If it has been selected, an input
265 on microprocessor 96 will be high. If microprocessor control has not
been selected, step 266 sets a mode flag MF to "5", signifying a power
down mode for microprocessor 96. The microprocessor then executes a mode
case select function 268, shown in detail in FIG. 5, and the program exits
at 270. If step 264 finds that microprocessor control has been selected,
step 272 checks to see if flag MF has been set to #5, signifying the
power-down mode. If flag MF is set to #5, step 274 executes an on/off
switch routine, and the program exits at 276. If flag MF is not set to #5,
the program checks a shutdown flag SDF to see if it is true, which would
indicate that some other program has requested that unit 20 be shut down.
If shut down flag SDF is true, step 280 executes a unit shut down
sequence, and the program exits at 276.
If shut down flag SDF is not true, step 282 checks to see if an engine
start flag ESF is true, and if it is, step 284 executes a Diesel engine
start routine, shown in detail in FIGS. 6A and 6B, and the program exits
at 276.
If flag ESF is not true, step 286 checks a pretrip flag PTF to see if a
pre-trip operation has been requested. The pre-trip operation causes a
plurality of system self checks to be made to determine if the unit is
ready for operation. If the flag PTF is true, step 288 sets mode flag MF
to #6, indicating that the pre-trip routine should be performed.
If flag PTF is not true, step 290 checks a manual defrost flag MDF to see
if it is true, and if it is, step 292 sets mode flag MF to #3, requesting
defrost. If flag MDF is not true, step 294 performs a manual defrost
decision block, which could result in the setting of flag MDF for
detection on the next run through the program.
Step 292 advances to step 292 which checks to see if a timed defrost flag
TDF is true, and if it is, , step 298 sets mode flag MF to #4, requesting
defrost. If timed defrost flag TDF is not true, step 300 performs a timed
defrost decision block, which could result in the setting of flag TDF for
detection on the next run through the program.
Step 300 advances to step 302 which checks to see if selector switch 174
has selected "cycle sentry", which is the mode in which the operative
prime mover 28 is started and stopped according to the condition of the
load in the served space 90. If the cycle mode has been selected, step 304
sets mode flag MF to #1, and the cycle sentry program shown in FIG. 11
will be run at the appropriate time.
If step 302 finds that the cycle sentry mode has not been selected, step
306 checks to see if the operative prime mover is the electric motor 32.
If the operative prime mover is engine 30, not electric motor 32 the
program goes to step 308, which sets mode flag MF to #2, indicating the
continuous operating mode. If step 306 finds that the drive is the
electric motor 32, step 306 further checks to see if the selected set
point temperature is at or below 24 degrees F., indicating a frozen load.
If the set point is above 24 degrees F., step 306 advances to step 308,
just described. If the prime mover is the electric motor 32, and the set
point indicates a frozen load, step 306 decides that the cycling mode
should be used, notwithstanding the position of selector switch 174, going
to step 304 which sets mode flag MF to #1, to indicate the cycling mode
should be used.
FIG. 5 sets forth the mode case select function 268 shown in block form in
FIG. 4. Function 268 is entered at 310 and step 312 checks to see if the
number of the mode flag MF is in the correct range of 1 through 6. If it
is not, step 314 sets flag MF to the default mode #2, which signifies the
continuous mode. The "yes" branch from step 312 and step 314 both go to
step 316 which determines the number of mode flag MF. The program goes to
function 318 when mode flag MF is #1, to run a cycling mode program, which
is shown in FIG. 11. The program goes to function 320 when mode flag MF is
#2, to run a continuous mode program, which is shown in FIG. 10. The
program goes to function 322 when mode flag CF is #3, to run a manual
defrost program; to function 324 when mode flag CF is #4 to run a timed
defrost program; to function 326 when mode flag CF is #5 to run a power
down program; and, to function 328 when mode flag CF is #6 to run a
pre-trip program.
Function 284 of FIG. 4, an engine start program, is shown in detail in
FIGS. 6A and 6B. As shown in step 282 of FIG. 4, the engine start program
is run when the engine start flag is true, and as will be hereinafter
described, the engine start flag is set true in the start-stop or cycling
mode program of FIG. 11.
The engine start program is entered at 330 of FIG. 6A and an initial
function of the program is to select an engine pre-heat time responsive to
engine temperature. Step 332 obtains the output of the engine coolant or
water temperature sensor (WTS) 116. Step 334 determines if the water
temperature sensor output is in a plausible range by comparing it with a
predetermined range preset in microprocessor memory 122. If the sensor
value is not in the predetermined range, step 336 sets an alarm code WTSF
for use by the operator or service personnel which indicates failure of
the engine water temperature sensor 116.
If the water temperature sensor value is in the proper range, step 338
determines if the sensor value exceeds a first predetermined temperature,
eg., 80 degrees F. or higher. If so, step 340 sets the engine pre-heat
time (PH) to a predetermined minimum value, eg., 20 seconds. If the
coolant temperature does not exceed the first predetermined value, step
342 determines if the coolant temperature is in a predetermined range,
between the first predetermined value and a second predetermined value,
eg., between 80 degrees F. and 20 degrees F. If the coolant temperature is
in this predetermined range, step 344 uses the temperature value to access
a look-up table stored in ROM 122. If step 342 finds the coolant
temperature is not in the predetermined range, then the coolant
temperature must be below the second predetermined value, e.g., 20 degrees
F., and step 346 assigns a predetermined maximum value to the pre-heat
time, e.g., 100 seconds. When step 334 finds that sensor 116 has failed,
the program advances from the alarm step 336 to step 346, which assigns
the maximum pre-heat time.
FIG. 7 is a graph which illustrates the preheat time determination, having
coolant temperature as determined by water temperature sensor (WTS) 116 on
the ordinate and pre-heat time PH on the abscissa. When the coolant
temperature is above a first predetermined value, indicated by broken line
335, the program assigns a predetermined minimum pre-heat time, indicated
by solid line 337. When the coolant temperature is below a second
predetermined value, indicated by broken line 339, the program assigns a
predetermined maximum pre-heat time, indicated by solid line 341. When the
coolant temperature is between the first and second predetermined values
335 and 339, the pre-heat time is obtained from a pre-heat look-up table,
indicated by solid line 343. As shown by line 343 in FIG. 7, the pre-heat
time is preferably a linear function of engine coolant temperature.
After the engine pre-heat time PH has been selected, step 348 energizes the
pre-heat relay 152 which has its associated set of normally open contacts
153 connected in parallel with the manually operated pre-heat switch 150.
The "microprocessor" position of selector switch 154 provides voltage to
pre-heat relay 152 from conductor 128 to conductor 155. The microprocessor
96 controls the various relays by providing a sinking current path. Thus,
when pre-heat relay 152 is energized, contacts 153 close and a circuit is
established through the glow plugs 148 which includes the battery 126 and
DC shunt 130. The engine reset switch 134 is not part of this circuit The
next function of program 282 is to protect the battery and wiring against
a fault in the glow plugs.
Step 348 includes a delay function, which delays reading the glow plug
current for 2 seconds, for example, until the glow plug current has
stabilized. Step 350 then checks the DC shunt reading, obtained via
conductors 194 and 196, to see if the glow plug current is in a
predetermined normal range, such as between -20 and -40 amperes, with the
negative signs indicating battery discharge. If the glow plug current is
not in the predetermined normal range, step 352 sets an alarm code GLOPL
indicating that the current is out-of-range, and step 354 determines if
the problem is causing excessive current flow. If the current is not
between the high end of the normal range and a predetermined maximum
allowable value, such as about -75 amperes, step 356 de-energizes the
pre-heat relay and sets the pre-heat time "elapsed". This protects the
battery and wiring, while allowing the engine to be started without
pre-heat. Step 358 updates a pre-heat timer in RAM 124, which keeps track
of pre-heat time, and step 360 checks timer PHT to determine when the
pre-heat time PH has elapsed.
A next function of the engine starting program is to determine if the
refrigerant circuit pressure is below a predetermined maximum allowable
value, before actual cranking of the engine is permitted. When the preheat
time PH has elapsed, step 362 energizes the run relay 158. Contacts 172 of
relay 158 close to energize the engine fuel solenoid FS via the
refrigerant high pressure cut-out switch (HPCO) 110. After a delay, such
as 2 seconds, to enable the system to stabilize, step 364 checks to see if
both sides of the high pressure cut-out switch are high. Microprocessor 96
checks the status of input conductors 200 and 202 to make this
determination. If the refrigerant pressure on the high pressure side of
the refrigerant circuit is not excessive, switch 110 will be closed and
both sides will have battery voltage.
If step 364 finds that both sides of switch 110 are not high, step 366
de-energizes the pre-heat relay 152, as the engine will not be started.
The program then goes into a diagnostic mode, to determine why both sides
of switch 110 are not high. Step 368 checks to see if both sides of switch
110 are low. If not, then switch 110 is open, indicating excessive
refrigerant pressure, and step 370 sets an alarm code indicating shutdown
is due to high refrigerant pressure. If both inputs are low, then voltage
has not been applied to switch 110, and step 373 sets an alarm code which
indicates failure of the run relay 158.
Steps 370 and 372 both go to step 374, with step 374 setting the engine
shutdown flag SDF and a modulation-valve-routine-complete flag MVCF true,
with the setting of flag MVCF true indicating that closing of the
modulation valve is not necessary since the engine will not be started.
Step 374 further sets engine start flag ESF false, since the engine has
not been started, and the program exits at 376.
When step 364 finds both sides of switch 110 high, indicating the
refrigerant pressure is not excessive, step 378 determines if a modulation
valve start feature has been selected, which feature closes the modulation
valve prior to engine cranking to reduce the load on the engine. If this
feature has been selected, step 380 initiates the running of the
modulation valve start routine shown in FIG. 8. If step 378 finds that the
modulation valve start feature has not been selected, step 382 sets
modulation-valve-routine-complete flag MVCF to 1, indicating the program
of FIG. 8 need not be run, it sets the modulation valve output 228 to
provide 0 current to modulation valve 64, which maintains modulation valve
64 fully open, and step 382 disables the heat, high speed and hot gas
relays 160, 162 and 166, respectively, to insure that the engine will
start the refrigeration system in a low speed, cooling cycle mode.
Step 382 advances to step 384, as does step 380, with step 384
de-energizing the shutdown relay 156 during engine cranking. Contacts 168
of shutdown relay 156 thus close to connect the reset switch SSW between
battery voltage and ground, with the time delay in the opening of contacts
134 upon excessive current functioning as a protective limit on engine
cranking time. After the engine has been successfully started, the
shutdown relay 156 will be energized, which is the fail-safe mode. With
the run relay 158 energized, the start relay 146 has voltage via conductor
175, and step 384 energizes start relay 146 by providing a sinking current
path via conductor 212. Step 384 also clears and starts a "start" timer ST
in RAM 124, which keeps track of cranking time. Start relay 146 closes its
set of normally open contacts 147 which energize starter solenoid (SS)
142. Starter solenoid 142 closes its set of normally open contacts 143 to
connect starter motor 140 to battery 126.
Step 386 updates start timer ST, and a first check on engine starting is
performed by steps 388 and 390, which allow the program to continue only
if the engine speed exceeds a predetermined first value, such as 40 RPM,
or the start time equals or exceeds a first predetermined period of time,
such as 3 seconds. Once either of these two events has occurred, the
program advances to step 392 to find out if this point in the program has
been reached due to the start timer ST reaching the predetermined first
time value, or due to the engine speed reaching the first predetermined
engine speed value.
If step 392 finds that the start timer ST reached the predetermined first
time value, either the engine did not start, or there is a problem, and
the program begins a phase to determine whether or not the engine started,
and if it did start, it provides diagnostics to indicate why steps 388 and
390 did not detect the start. Step 394 energizes the shutdown relay 156 to
prevent the reset switch SSW from operating, which would remove voltage
from conductor 128 and shut the unit down. Step 394 further de-energizes
the start and pre-heat relays, as no further attempt to start the engine
will be made, if indeed it did not start.
Step 396 delays for a short period of time to allow the engine to
stabilize, if it did start, and step 398 then checks input conductor 198
to see if the low oil pressure switch (LOPS) 192 has opened, indicating
oil pressure If this input is not high, then there is no oil pressure, and
step 400 sets an alarm code FCRNK which indicates that the engine failed
to crank. If input 198 is high, the low oil pressure switch is open, and
the engine either started or switch 192 is defective. Step 402 checks
input conductors 194 and 196 for the polarity of the battery current. If
the polarity is not positive, we have two additional indications that the
engine did not start, ie., low oil pressure and lack of alternator output,
and step 404 sets an alarm code OPS which indicates the low oil pressure
switch 192 is defective.
If step 402 finds the charge amperes positive, it indicates the alternator
138 is being driven by engine 30. Thus, engine 30 started and the faulty
sensor is the engine speed or RPM sensor 118, and step 406 sets an alarm
code RPMF indicating that sensor 118 is faulty. Step 406 also sets an RPM
sensor fail flag RPMSFF true. Step 408 checks
modulation-valve-routine-complete flag MVCF to determine if the modulation
valve routine has been completed, and if it has not, the program exits at
416. If flag MVCF has been set true, step 410 sets a unit-running-flag URF
true and step 412 sets flag MVCF true and engine start flag ESF false,
with the latter indicating that the engine need not be started, since it
is running. Steps 400 and 404 both proceed to step 412 via a step 414
which sets engine shutdown flag ESF true. The setting of the engine start
flag false in step 412 now means that the engine need not be started,
because it failed to start properly.
If program step 392 finds that this point of the program was reached
because the engine RPM sensor 118 reached the first predetermined speed,
eg., 40 RPM prior to the expiration of the first predetermined period of
time, eg., 3 seconds, then step 418 updates the start timer ST and the
program advances to a second starting phase, implemented by steps 420 and
422, which phase is not passed until either the engine speed reaches or
exceeds a second predetermined value, eg., 800 RPM, determined by step
422, or the start timer ST reaches or exceeds a second predetermined
value, eg., 30 seconds, determined by step 420.
Upon passing this second starting phase, step 424 determines if the start
timer ST equals or exceeds the second predetermined period of time, and if
not, it indicates the engine speed has passed the second predetermined
value and has started properly. Step 424 goes through the hereinbefore
described steps 408, 410, and 412, when step 424 finds a successful engine
start. When step 424 finds that the program reached this point because the
start timer ST reached the second predetermined period of time, then the
program performs diagnostics similar to those described starting with step
398. Step 426 energizes the shutdown relay 156, and de-energizes the start
and pre-heat relays 146 and 152. Step 428 delays for a short time to
enable the system to stabilize, in the event the engine did start, and
step 430 checks for oil pressure. If the oil pressure is low, indicating
the engine did not start, step 432 sets an alarm code FSTRT which
indicates the engine failed to start. Step 400 set an alarm code FCRNK
which indicated the engine failed to crank, but since the first starting
phase was successfully passed, the engine did indeed crank, but by failing
the second phase it indicates that although it cranked, it failed to
start.
If step 430 finds the oil pressure input high, step 434 checks to see if
the charge amperes are positive, indicating alternator 138 is being driven
by prime mover arrangement 28. If the charge amperes are not positive,
step 436 sets alarm code OPS indicating failure of the low oil pressure
switch 192, step 438 sets the engine shutdown flag SDF true, and the
program goes to step 412. If the charge amperes are positive, it indicates
engine 30 has started, and the program goes to step 406, hereinbefore
described, which sets alarm RPMF indicating failure of the engine RPM
sensor 118. The program then advances through the hereinbefore described
steps 410 and 412 to the program exit 416.
The modulation valve start routine function 380 shown in block form in FIG.
6A is shown in detail in FIG. 8. This function is entered at 440 and step
442 sets the modulation valve routine complete flag (MVCF) false. Steps
444 and 446 make sure the engine will start in a low speed cooling mode,
by disabling the high speed, heat and hot gas relays 162, 160 and 166,
respectively. Step 448 then outputs the value of current required to fully
close modulation valve 64, eg., 1.2 amperes for a typical valve. Step 450
clears and starts a modulation valve timer (MVT) in RAM 124. Step 452
updates timer MVT and step 454 determines when timer MVT reaches a
predetermined period of time, such as 15 seconds. Step 456 updates timer
MVT and initiates a linear decay of modulation valve current to a
predetermined value, such as 600 ma. Step 458 determines when timer MVT
reaches a predetermined period of time, such as 45 seconds, and then step
460 drops the modulation valve current to zero, to fully open the valve.
Step 462 continues to update timer MVT, and when the time reaches a
predetermined value, such as 60 seconds, as detected by a step 464, step
466 checks to see if the cycling mode has been selected, and if so, the
modulation valve 64 is disabled, as it is only used in the continuous
mode. Step 468 sets flag MVCF true, and the program exits at 470.
FIG. 9 is a graph which sets forth some of the functions of the modulation
valve start routine 380 shown in FIG. 8, plotting modulation valve current
on the ordinate and MVT time on the abscissa The modulation valve current
starts at a predetermined level 472, to fully close valve 64. After a
predetermined first period of MVT time, indicated at point 474, a linear
decay in current magnitude is initiated with the linear decay being
illustrated with straight line 476. When the MVT time reaches a second
predetermined period of time, indicated at point 478, the valve current is
reduced to 0.
In FIG. 5, when step 316 found mode flag MF set to #2, the "continuous"
mode program 320 was run. The continuous mode program 320 is set forth in
detail in FIG. 10. Program 320 is entered at 480 and step 482 deenergizes
the run relay 158. If the unit 20 is running, switch 174 in FIG. 2B will
provide voltage to conductor 385 via the "continuous" position of switch
174 and the normally closed contacts 170 of the run relay 158. Step 484
checks to see if unit 20 is indeed running, such as by checking its input
265 for voltage. If unit 20 is not running, step 486 updates a
unit-not-running timer (UNRT) in RAM 124. Step 488 determines if timer
UNRT has reached a predetermined value, such as 5 minutes If this
predetermined time has not been reached, the program exits at 490, and the
program will continue to exit each time it is run until step 488 finds
timer UNRT has reached the predetermined period of time. Step 488 then
goes to step 492 which sets the unit shutdown flag SDF true, step 494 sets
an alarm code ENRUN which indicates the prime mover 28 is not running, and
the program exits at 490.
When step 484 finds the unit running, step 500 checks to see if a condition
flag CF has been initialized. If this flag has not been initialized, it
indicates the unit has just been turned on, and step 502 checks to see if
the value of the selected temperature sensor, ie., either return air
sensor 100 or discharge sensor 104, is greater than the selected set point
temperature. If it is, step 504 sets condition flag CF to call for a low
speed cooling (LSC) mode. If the sensor temperature does not exceed set
point, step 506 sets condition flag CF to call for a low speed heating
(LSH) mode.
If step 500 finds condition flag CF initialized, unit 20 has been running
and one of the refrigerant operating conditions has already been selected
for unit 20. Step 508 then checks a modulation-valve-present flag (MVPF)
to see if jumper 206 shown in FIG. 2B is in or out. If jumper 206 is out,
flag MVPF will be false, and the continuous mode will be run without
suction line modulation. Step 514 sets a modulation flag MVF false, to
indicate there will be no suction line modulation. If jumper 206 is in,
flag MVPF will be true and step 510 checks the set point temperature to
determine if the load being conditioned in space 90 is a fresh or a frozen
load. If step 510 finds the set point is not greater than 24 degrees F.,
for example, the load is frozen and suction line modulation should not be
used, notwithstanding that jumper 206 is in and flag MVPF is true, so step
510 goes to step 514 to set flag MVF false. If step 510 finds a fresh load
is being conditioned, step 510 goes to step 512 to set flag MVF true,
indicating the continuous mode is with suction line modulation.
Steps 504, 506, 512 and 514 all go to step 516 which sets temperature
limits for the operative control algorithm. Step 518 then runs a
"condition case" program, which simply determines which operational mode
has been selected by the condition flag CF, eg., high speed cool, low
speed cool, low speed heat and high speed heat. Step 520 sets the unit not
running timer UNRT to 0 and the program exits at 522.
In FIG. 5, when step 316 found the mode flag set to #1, the "cycle" mode
program 318 was run. The cycle sentry or start-stop mode program 318 is
set forth in detail in FIG. 11. The cycle sentry program 318 is entered at
524 and step 526 sets the modulation flag MVF false, and modulation
related values such as integral error and floor limit error are set to 0,
since suction line modulation is not used during the cycle mode. Step 526
also clears the unit not running timer UNRT. Step 528 then checks to see
if the condition flag has been initialized If it has not, unit 20 has just
been turned on and step 528 goes to step 530 to determine if the load in
load space 90 is fresh or frozen If the load is fresh the set point
temperature will be above 24 degrees F., and step 530 goes to step 532 to
determine the temperature of space 90 relative to set point. If the
operative load temperature sensor detects that the load temperature is
greater than set point, step 534 sets the condition flag CF to indicate
that the unit should operate in a low speed cool mode. If step 532 finds
the load temperature is less than set point, then step 536 sets the
condition flag CF to indioate the unit should run in low speed heat. Steps
534 and 536 both go to step 538 which sets the engine start flag ESF true,
indicating the engine should be started by the engine start program
described relative to FIGS. 6A and 6B. Step 540 sets the temperature
limits for the relevant control algorithm, step 542 checks the condition
flag CF to determine the proper operative mode of the selected control
algorithm, and the program exits at 544.
If step 530 finds the load space 90 contains a frozen load, step 530 goes
to step 546 which checks the load temperature relative to the selected set
point temperature. If the load temperature is above set point, step 546
goes to the hereinbefore described step 534 to set condition flag CF to
call for a low speed cool operative condition. If the load temperature is
below the selected set point temperature, step 548 determines if the
engine coolant temperature is warm enough to allow the engine to remain
off. For example, step 548 checks sensor 116 to see if the engine coolant
temperature is above 35 degrees F. If it is not, then step 548 goes to the
hereinbefore described step 536 which sets condition flag CF to call for
low speed heat, and step 538 sets the engine start flag ESF true to call
for an engine start.
If the engine coolant temperature is above the predetermined temperature,
eg., 35 degrees F., then engine 30 may remain off and step 548 goes to
step 550 which sets condition flag CF to call for a null condition. Step
550 then goes to the hereinbefore described step 540, by-passing step 538,
as engine start flag ESF should not be set true.
If step 528 finds the condition flag CF initialized, step 552 checks to see
if unit 20 is running, a prime mover 30 or 32 is driving compressor 26. If
it is not running, step 554 checks to see if it should be running by
checking the condition of a null flag NF. If flag NF is true, engine 34
should not be running and step 554 goes to step 540 to set the temperature
limits, step 542 selects the desired operative condition from the setting
of condition flag CF, and the program exits at 544. If flag NF is not
true, the engine should be running and step 554 goes to step 538 to set
engine start flag ESF true, and then the program goes through steps 540
and 542, exiting at 544.
FIG. 12 is a control algorithm for the cycle sentry mode, which is used
when the selected set point temperature is above 24 degrees F., indicating
a fresh load, and the operative sensor is the return air sensor 100. When
the temperature of the load space 90 is falling, the left-hand side of the
algorithm is utilized, and when the temperature is rising the right-hand
side of the algorithm is used. The various operating modes are the
different modes which are indicated by the condition flag CF, and selected
in steps 518 and 542 of the continuous and cycle programs 320 and 318,
respectively.
Assuming that the load space is in initial temperature pull down, the
operative mode will be high speed cool, not-in-range, until the load
temperature as indicated by return air sensor 100 indicates a value 5
degrees F. above set point. A high speed cool, in-range program will then
be run until sensor 100 indicates the selected set point temperature has
been reached, at which point the engine 30 may be turned off, if the
engine coolant temperature is high enough, as described relative to step
548 in FIG. 11, to enter a null condition.
The microprocessor 96 "remembers" whether each null condition is entered
from a cooling mode or from a heating mode by running two different null
programs which will be called NULLDC when null is entered from a cooling
mode, and NULLDH when null is entered from a heating mode. If the load
temperature continues to drop and reaches a temperature error relative to
set point of -3.5 degrees F, with the minus sign (-) indicating the load
temperature is below set point, a low speed heat, in-range program is
called for, and if the temperature error drops to -6.8 degrees F., a high
speed heat, not-in-range program is called for.
If the load temperature is rising from high speed heat, not-in range, when
the return air temperature error is -5 degrees F., the program calls for a
high speed heat, in-range program. When the temperature error reaches -1.7
degrees F., a low speed heat, in-range program is called for, and when the
temperature error reaches +1.7, with the positive sign (+) indicating
above set point, the NULLDH program is called for, which turns engine 30
off. If the temperature error rises to +5.1 degrees, the engine will be
started in a low speed cool mode, and if the temperature error continues
to rise to 8.5 degrees F., the high speed cool, not-in-range program will
be called for.
When the temperature is falling and the NULLDC range is exceeded by the
negative error reaching the lower limit of NULLDC, and the refrigeration
unit's operating mode is changed to low speed heat, in-range, a timer in
RAM 124 may be started, such as an 8 minute timer, for example. If the
return air temperature does not reach an error of -1.7 degrees F. within 8
minutes, with an error of -1.7 degrees F. being the temperature which
initiates low speed heat during a rising temperature, the high speed heat,
in-range program may be initiated. The high speed heat mode will then
remain in control until the NULL zone is reached.
In like manner, when the temperature is rising and NULLDH changes to low
speed cool, in-range, a timer may be started, such as an 8 minute timer,
for example, and if the return air temperature does not reach an error of
+3.5 degrees F. within 8 minutes, with +3.5 degrees F. being the error
temperature which initiates low speed cool during a falling temperature,
the high speed cool, in-range program may be initiated, which will then
remain in control until the NULL zone is reached at set point.
FIG. 13 sets forth a control algorithm which may be used in the cycle
sentry mode when the set point is set below 24 degrees F., ie., the load
is frozen, and the operative sensor is the return air sensor 100. With a
falling temperature, high speed cool, not-in-range is the operative
program until a temperature error of +5 degrees F. is reached, at which
time the high speed cool, in-range program is called for. When set point
is reached, the NULLDC program may be called for, or a low speed heat, in
range program may be called for, depending upon whether heat is locked out
by a selectable control option.
Upon a rising temperature, the low speed heat option would call for NULLDH
at an error temperature of +1.7 degrees F. and for low speed cool,
in-range at an error temperature of +5.1 degrees F. At an error of +8.5
degrees F., the high speed cool, not-in-range program would be called for.
When the error +5.1 degrees F. is reached during a rising temperature, a
timer, such as a 12 minute timer, for example, may be set, which would
give the low speed cool program 12 minutes to reach an error temperature
of +3.5, or otherwise trigger high speed cool, which would then remain in
control until set point is reached.
FIGS. 14A and 14B may be combined to provide a program 560 for the
hereinbefore mentioned operating condition NULLDC, which program is called
when the null condition is entered from a cooling cycle. Program 560 is
entered at 562 and step 564 checks a run flag RF to see if unit 20 is
running. If unit 20 is not running, step 566 checks the input from engine
coolant sensor 116 to see if the engine should be started because its
temperature dropped below a predetermined value, such as 35 degrees F. If
the coolant temperature is below the predetermined value, step 568 sets
the engine start flag ESF true, to signify that the engine should be
started.
Step 570 then determines whether the engine should be started in a heating
cycle or a cooling cycle, by checking the temperature of the conditioned
space 90 relative to the set point temperature. This is quickly checked by
determining whether the error between the load temperature and the set
point temperature is positive or negative. If step 570 finds the error
negative, ie., the load temperature is below or "colder" than set point,
and step 572 sets condition flag CF to the "next potential low". The term
"next potential low" means the unit operating condition which is just
below the present operating condition on the left-hand side of the
pertinent control algorithm. Using the control algorithm of FIG. 12 as an
example, since the present operating condition is NULLDC, the next
operating condition in the lower direction would be low speed heat, with
or without the hereinbefore mentioned 8 minute timer, as desired.
If the error is positive, ie., the load temperature is above or "warmer"
than set point, and step 574 sets condition flag CF to the "next potential
high". The term "next potential high" means the unit operating condition
which is just above the present operating condition on the right-hand side
of the pertinent control algorithm. For example, since the present
operating condition is NULLDC, the next operating condition in the upper
direction on the control algorithm of FIG. 12 would be low speed cool,
with or without the hereinbefore mentioned 8 minute timer, as desired.
If step 566 finds the engine temperature is greater than the predetermined
temperature, eg., 35 degrees F., the engine does not have to be started
because it is getting cold and step 566 goes to step 576 which compares
the error between load temperature and set point with the "low trip
point". The term "low trip point" means the error on the pertinent control
algorithm at the low side of the current operating condition which
triggers the next lower operating condition. Using the algorithm of FIG.
12 as an example, the "low trip point" for the operating condition NULLDC
is -3.5. If step 576 finds the error is below than the low trip point on
the control algorithm, the load temperature has dropped out of the range
of the current operating condition and step 578 sets condition flag CF to
the next potential low, which would be low speed heat in the control
algorithm of FIG. 12.
If step 576 finds that the error is not below the low trip point, step 580
determines if the error is greater than, ie., above the "high trip point"
on the control algorithm. The term "high trip point" means the error on
the pertinent control algorithm at the high side of the current operating
condition which will trigger the next higher operating condition. Using
the algorithm of FIG. 12 as an example, the "high trip point" for the
operating condition NULLDC is +5.1. If step 580 finds the error is greater
than the high trip point, the load temperature has risen out of the range
of the current operating condition and step 586 sets the condition flag CF
to the next potential high, which would be low speed cool in the control
algorithm of FIG. 12.
If step 580 finds the error is not greater than the high trip point, the
error is thus still within the range of the current operating condition
and step 580 goes to step 582 which turns on display elements which
indicate the load temperature is "in-range", and step 584 sets null flag
NF true, to indicate that the unit should be in null.
Steps 578 and 580 both proceed to step 588 which sets engine start flag ESF
true, to indicate engine 30 should be started. Step 588 and steps 572 and
574 all proceed to step 590 which sets a condition timer CT in RAM 124 to
zero. Condition timer CT times how long the unit has been in each new
operating condition, to insure that the unit remains in each operating
condition for a predetermined minimum period of time, eg., 10 seconds,
before going to another operating condition Step 592 goes to step 594, as
does step 584, with step 594 setting a heat timer HT in RAM 124 to 0. The
purpose of heat timer HT will be hereinafter explained. The program exits
at 596.
If step 564 finds the engine running, step 564 goes to step 598 which
checks to see if the battery charging current exceeds a predetermined
value, eg., 8 amperes, indicating the current battery condition is such
that the engine should not be stopped. If step 598 finds the battery
charging current exceeds the predetermined value, step 600 performs a
"forced trip" routine, ie., step 600 keeps the engine running. Step 6.02
sets heat timer HT to 0, and the program exits at 604. The forced trip
routine of step 600 sets null flag NF to 0, indicating the unit should not
stop, and it sets condition flag CF to either the next potential low or
the next potential high, using the value and polarity of the error between
the load temperature and set point to make the determination.
If step 598 finds the battery charging current is less than the
predetermined value, step 598 goes to step 606 which checks the input
provided by engine coolant sensor 116 to see if engine 30 is warm enough
to turn off, ie., above a predetermined temperature such as 90 degrees F.
Step 566 started the engine when the temperature dropped below 35 degrees
F., for example, and step 606 makes sure the engine is above 90 degrees
F., for example, when it stops. This difference between the engine
starting and stopping temperatures insures that engine 30, once turned
off, will not be quickly started again due to step 566. If step 606 finds
the engine coolant temperature below the predetermined value, step 606
goes to step 600 to continue running engine 30.
If step 606 finds the temperature of the engine coolant warmer than the
predetermined temperature, step 608 determines if the load temperature
versus set point temperature error is below the low trip point If so, step
610 sets condition flag CF to the next potential low condition, step 612
sets condition timer CT to 0, step 614 sets null flag NF to 0, step 616
sets heat timer HT to 0, and the program exits at 618. If step 608 finds
the error is above the low trip point, step 620 determines if the error
exceeds the high trip point. If it does, step 622 sets condition flag CF
to the next potential high, and the program continues to the hereinbefore
described step 612.
If step 620 finds the load temperature versus set point error is not above
the high trip point, the load temperature is in the range of NULLDC, and
the engine may be stopped. Before stopping the engine, however, step 624
checks a null heat flag NHF to see if it is set. Flag NHF is set to select
a program option which, when unit 20 enters null from a cooling cycle,
causes unit 20 to switch from cool to heat for a short period of time just
long enough to warm the evaporator coil 62. Entering null with a cold
evaporator may cause the "cold" from the evaporator to affect the
operative temperature sensor and cause premature starting of engine 30.
If the null heat option has been selected, ie., flag NHF is true, step 624
goes to step 626 which checks the hereinbefore mentioned heat timer HT, to
see if it has reached or exceeded a predetermined value, e.g., 10 seconds,
selected as the time for the unit to be in a heating cycle, before
entering the null mode from a cooling cycle. At this point in the program,
heat timer HT will be 0 and the program checks to see if the heat relay
160 is energized. At this point in the program heat relay 160 will not be
energized, and step 630 energizes heat relay 160 and it clears and starts
heat timer HT. Step 632 updates heat timer HT, step 634 turns on display
elements to indicate "in-range", ie., that the load temperature is in the
"null" range, step 636 sets null flag NF true, indicating the load
temperature is in the "null" range, and the program exits at 618. The next
time through the program, step 628 will find heat relay 160 energized and
proceed to step 632, to update heat timer HT. When step 626 finds heat
timer HT has reached the predetermined value, eg., 10 seconds, step 626
goes to step 638 which checks condition timer CT to make sure that unit 20
has been in the present operating condition for the predetermined time,
eg., 10 seconds in this example. If the predetermined value of condition
timer CT is longer than the predetermined value of heat timer HT, then
step 638 may find that condition timer CT has not reached the
predetermined value, and step 638 would proceed to step 640 which updates
condition timer CT.
When condition timer CT reaches the predetermined value, step 638 goes to
step 644 which de-energizes the run relay 158 to stop engine 30 by
removing voltage from the fuel solenoid FS. Step 646 sets condition timer
CT equal to the predetermined value, and the program goes through the
hereinbefore mentioned steps 634 and 636 to the program exit 618.
If step 624 finds that the null heat option has not been selected, ie.,
flag NHF is false, step 624 goes to step 648 to check the value of
condition timer CT. If condition timer CT has not reached the
predetermined value, step 650 updates condition timer CT. If step 648
finds condition timer CT has reached the predetermined value, step 652
de-energizes the run relay 158, and step 654 sets condition timer CT to
the predetermined value. Step 654 and step 650 both go to step 658 which
turns on "in-range" display elements, step 660 sets null flag NF true,
step 662 sets heat timer HT to 0, and the program exits at 618.
The program for NULLDH is similar to the program for NULLDC, except steps
624 through 646 related to the null heat option are omitted, since NULLDH
is entered from a heating cycle and the evaporator will already be warm.
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